1. Field of the Invention
The present invention relates to a camera system capable of focus detection by means of receiving light through an interchangeable objective lens. More particularly, it relates to an improvement of the above-mentioned system and also to an improvement of the camera body and the interchangeable objective lens in that system.
2. Description of the Prior Art
Conventionally, a camera system has been proposed wherein the focus adjustment and the display of detected focus condition are controlled in accordance with a signal based on the light which has passed through the interchangeable objective lens and received by light receiving device provided in the camera body.
Generally, according to the camera system, a number of different types of interchangeable lenses can be mounted on a camera body, and one interchangeable lens can be mounted on a number of different types of camera bodies. In other words, according to the camera system to which the present invention pertains, there is a compatibility between a number of camera bodies and a number of interchangeable objective lenses, enabling a number of combinations of a camera body and an interchangeable lens.
In the camera system described above, there are a number of problems to be solved when the focus detection and focus adjustment are to be carried out with a signal based on the light which has passed through the interchangeable objective lens. A problem in the case of focus detection is, for example, the change in conditions, such as in the optical arrangement, every time when the combination of camera body and interchangeable lens changes. To establish a camera system of the above described type which can effect the focus detection with a high accuracy, it is necessary to consider all the possible conditions set up by various combinations, or otherwise, a high reliability on the focus detection can not be ensured. For example, when the fully open aperture size of an interchangeable lens is smaller than a predetermined size, there may be a case wherein a required focus detection can not be carried out properly. Such a case will be described later in connection with FIGS. 1 to 3.
A problem in the case of focus adjustment carried out automatically by the motor drive of focusing lens in the interchangeable lens in accordance with the result of focus detection is in the driving source and its control. For example, the control of driving source according to even the same result of focus detection would have to vary depending on the various combination of camera body and interchangeable lens changes.